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Magnetized filamentary gas flows feeding the young embedded cluster in Serpens South


Observations indicate that molecular clouds are strongly magnetized, and that magnetic fields influence the formation of stars. A key observation supporting the conclusion that molecular clouds are significantly magnetized is that the orientation of their internal structure is closely related to that of the magnetic field. At low column densities, the structure aligns parallel with the field, whereas at higher column densities, the gas structure is typically oriented perpendicular to magnetic fields, with a transition at visual extinctions AV 3 mag. Here we use far-infrared polarimetric observations from the HAWC+ polarimeter on SOFIA to report the discovery of a further transition in relative orientation, that is, a return to parallel alignment at AV 21 mag in parts of the Serpens South cloud. This transition appears to be caused by gas flow and indicates that magnetic supercriticality sets in near AV 21 mag, allowing gravitational collapse and star cluster formation to occur even in the presence of relatively strong magnetic fields.

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Fig. 1: The Serpens South cloud and its magnetic field.
Fig. 2: Filament and magnetic field orientations.
Fig. 3: Distribution of relative orientations of the FIL2 gas filament with respect to Bpos as a function of AV.
Fig. 4: Debiased polarization fraction as a function of the total intensity.

Data availability

The HAWC+ data that support the plots within this paper and other findings of this study are available from the SOFIA data archive at under project code 05_0206 or from the corresponding author upon reasonable request.

Code availability

The source code for POLARIS and PolarisTools used in this paper and written by S.R. are publicly available at


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Based in part on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract 50 OK 0901 to the University of Stuttgart. Financial support for this work was provided to T.P. by DLR through award number 50 OR 1719. D. Dowell, the SOFIA HAWC+ team, the SOFIA flight and ground crews, and the USRA SOFIA Project teams developed the SOFIA observatory, the HAWC+ instrument, performed the airborne observations, processed and calibrated the data, and delivered science-ready data products. D.P.C. acknowledges support funder NSF AST 18-14531, USRA SOF_4-0026 and NASA NNX15AE51G. D.S. acknowledges the support of the Bonn-Cologne Graduate School, which is funded through the German Excellence Initiative and funding by the Deutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center SFB 956 Conditions and Impact of Star Formation (subprojects C5 and C6). G.A.P.F. is partially supported by CNPq and FAPEMIG. This research has made use of data from the Herschel Gould Belt survey (HGBS) project ( and ref. 16).

Author information




T.P. led the SOFIA proposal, data analysis, interpretation of the data and the paper writing. The other authors contributed to the writing of the manuscript. D.P.C., S.R., P.C.M. and J.K. participated in the data analysis. E.L.-R. led the SOFIA data reduction. F.O.A. and G.A.P.F. conducted near-infrared polarization observations. K.S. provided the published near-infrared polarization data used in this study. J.H., K.M.M., F.N., D.S. and H.W. provided expertise in molecular cloud studies.

Corresponding author

Correspondence to Thushara G.S. Pillai.

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Pillai, T.G., Clemens, D.P., Reissl, S. et al. Magnetized filamentary gas flows feeding the young embedded cluster in Serpens South. Nat Astron 4, 1195–1201 (2020).

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